If this is your first visit, be sure to
check out the FAQ by clicking the
link above. You may have to register
before you can post: click the register link above to proceed. To start viewing messages,
select the forum that you want to visit from the selection below.

Welcome to Mac-Forums! Join us to comment and to customize your site experience! Members have access to different forum appearance options, and many more functions.

I bought a 2 Tb hard disk to make a backup from my windows PC that i was using at work. I divided the hard disk in two partitions and formatted them both in FAT32 format. This was done on a windows machine. The hard disk is connected by a USB-interface

I later decided that one of those partitions i wanted to use for Time-machine to backup my macbook pro (OSX 10.6.4). I thought i was better to use a MAC-format for this, so i wanted to re-format one of the partitions.

On the MAC, i used disk utitlity to ERASE the second partition and format it according the MAC OS extended (journaled). This was not successful and in finder I could no longer see the second partition. At THAT moment, I could still see the first partition. To verify my data on the first partition, I wanted to check it by connecting it to a Windows machine. The hard disk was recognized (or at least the controller), but BOTH partitions were not visible. Trying on my MAC, the first partition is ALSO no longer visible. This means I cannot see any data!

I am not sure what went wrong and if i can still salvage the data of the first partition. My guess is, something went wrong in the Master Boot Record, but I do not have much experience with this and i am afraid that any quick repair attempt, can make things worse.

I'm not sure you can retrieve that data. From what you posted, I'll try to figure out what happened.... First, you must have used third party software to partition and format that 2 TB hard drive as the Windows disk manager will not format any drive or partition greater than 32 GB to FAT-32.

When you used Disk Utility to erase the second partition and then format it as HFS+ and it wasn't successful, it may have created an EFI partition at the beginning of drive overwriting the Windows partition table. Now, the drive can not be seen by Windows. I don't understand why Disk Utility can not see it unless it's unformatted and unallocated. (Which may have happened)

Here's what I suggest: Unless the lost data is critical, it might be best to attach it to your Mac and use Disk Utility to partition and format the drive.
In other words, start over.

Create two partitions. Format the first partition as HFS+ extended journaled (required for Time Machine use) and the second partition as FAT-32. But be very careful about formatting the second partition. Disk Utility will default to formatting using the GUID scheme. That will cause problems. Instead, choose Options from below and format the second partition using the MBR scheme. That works best for FAT-32 partitions.

I forgot to write that indeed some of the data of the first partition is rather critical. It not only contains data that is a backup, but also data that was moved to there and does not exist anymore on any other location. So, i am looking for a way to retrieve the data.

Indeed I used third party software: EASEUS Partition Master for windows, to format the disk initially.

In order to retrieve the data, you'll need some good recovery software. I suggest trying the trial version of Data Rescue 3. If it looks like it will work to retrieve the data, buy a license. It's a bit steep ($99) but well worthwhile especially if the data is critical.

I don't know anything about the EASEUS Partition Master software except that it's free, so I can't comment on its effectiveness. I personally use an older version of Partition Magic which seems to work well, or Acronis software.